For monitoring and, if necessary, controlling the combustion properties in combustion processes, there is a need for recording at least one measure of the particle concentration in the exhaust gas of combustion processes. In particular, there is a need for recording at least one measure for the particle concentration in the exhaust gas of internal combustion engines, especially Diesel internal combustion engines.
The term particle concentration is mirrored in the following with the same meaning as particle mass or particle quantity. Reference will only still be made to particle mass. If the combustion process occurs in an internal combustion engine, which is preferably situated in a motor vehicle, what is of interest is the particle mass or the particle quantity which has been obtained on a predefined path.
A particle sensor has become known, for example, from German Patent Application No. DE 101 33 385, which includes a collecting chamber that is able to be connected to an exhaust gas stream of an internal combustion engine. On the upper side of the collecting chamber there is situated a first electrode. At the lower side, that is, opposite the first electrode, a second electrode is situated. The collecting chamber between the two electrodes is hollow. When the known sensor is in operation, particles, especially soot particles, arrive in the collecting chamber and deposit in the hollow space between the two electrodes. The at least slightly conductive particles bridge the intervening space between the two electrodes, so that there is a change in the impedance of the particle sensor. The impedance or the change with time of the impedance may be valued, and it is a measure for the load or the increase in load of the particle sensor with particles. Since the measuring effect is based on a collection of particles, the particle sensor may be designated as an integrating particle sensor.
Another particle sensor is described in German Patent Application No. DE 101 33 384. In this particle sensor the two electrodes are situated on one side of a collecting chamber, and mate in the shape of a comb. In this integrating particle sensor, too, the impedance and/or its change between the two electrodes may be drawn upon as a measure for the particle mass in the exhaust gas that has appeared on the path in a predefined time.
With the aid of experiments, it has turned out that the known particle sensors, especially the integrating particle sensors, for instance, resistive particle sensors, have cross sensitivities which, when there is a change in the conditions of the combustion process, may lead to influencing the particle sensor signal.